Almost every slab in Dallas–Fort Worth has moved. That is not alarmism, it is the consequence of building on Blackland Prairie clay. So the useful question is never "has my foundation moved" — it has — but "has it moved enough, in the wrong shape, to be doing damage, and is it still moving." Those are different questions with different answers, and the gap between them is where most of the money in this industry gets made and lost.
Why North Texas houses crack
The soil under most of the metroplex is a vertisol: clay defined by its shrink-swell behaviour rather than a soil that happens to exhibit it. The dominant series, Houston Black, is the official state soil of Texas and one of the most studied expansive soils in North America. Its official description puts crack widths at half an inch to four inches at a depth of a foot, open for 90 to 150 cumulative days in a normal year (Home Inspection Dallas). That is an ordinary year, not a drought. The clay is very deep, more than 80 inches, and its permeability is very slow, which means water enters fast through the cracks and then sits.
The Texas Section of ASCE defines expansive clay as soil with a weighted plasticity index above 15, or a maximum potential volume change greater than one percent (Texas Section ASCE). In the Tarrant County soil survey engineering tables, Houston Black, Heiden, Ferris and Slidell all carry plasticity indices of 28 to 42 (Soil Survey of Tarrant County). They clear the threshold by a factor of two or more. The same survey shows sandy soils in the Cross Timbers areas — Silawa at 4 to 14 — that barely move at all. Two houses eight miles apart in the same county can sit on soils with radically different behaviour, which is why a neighbour's experience is weak evidence about your house.
The same document notes that the majority of foundations built in Texas are shallow, stiffened, reinforced slab-on-ground. A shallow foundation on deep reactive clay is a structure sitting on something that changes volume seasonally underneath it. It is designed to accommodate that, not to prevent it.
The two shapes of movement
Movement matters less than the shape of the movement. North Texas houses cycle between two patterns, and knowing which one you have tells you where to look.
Centre lift, or doming. The soil around the perimeter dries and shrinks while the soil beneath the middle of the house stays comparatively moist — it is shaded and sheltered from evaporation. The slab effectively arches over a high centre. Cracking concentrates near the perimeter, and doors and windows in exterior walls bind.
Edge lift, or dishing. The perimeter soil becomes moist and swells, lifting the edges relative to the centre. Cracking concentrates toward the interior of the house.
Most North Texas houses do both, in alternation, across a year. This is the single most important thing to understand before you take a bid: a crack that visibly narrows or closes after a wet period is behaving like soil-moisture-driven seasonal movement, not like a static structural defect. A crack that only ever widens, across multiple seasons, is telling you something different.
What is normal, and what a tolerance actually means
Foundations are not built level. The construction tolerance widely accepted for slab-on-ground foundations is plus or minus three quarters of an inch, attributed to ACI 117 — meaning a house can have a full inch and a half of elevation difference from the day it was poured and still be within tolerance (Post-Tensioning Institute).
Read that again before anyone shows you a floor elevation map with a red zone on it. An inch of variation across a room is not, on its own, evidence of anything. The commonly used performance criteria are tilt of one percent — one inch in a hundred — and deflection of L/360, one inch in 360 inches. And even when those are exceeded, the same guidelines say there must be noteworthy distress correlated with the out-of-tolerance condition. Without correlated distress, it does not qualify as a deficiency in foundation performance.
The corollary is blunt: if you have a difference in floor elevation but no accompanying distress — no sheetrock cracks, no brick cracks, no out-of-square doors, no material separations — the out-of-level condition is most likely original construction, not movement.
One more piece of context that gets left out of sales conversations: most foundations and superstructures go through an initial 12 to 24 month adjustment period after occupancy, as yards, landscaping and watering programs get established. A two-year-old house with a hairline seam crack is doing what two-year-old houses do.
Signs that actually warrant attention
None of these individually proves a foundation problem. Together, and especially when progressing, they justify paying someone qualified to look.
Progression across seasons. This is the strongest single indicator. Not the presence of a crack — the growth of one through a full wet-dry cycle.
Stair-step cracking in brick veneer mortar joints, particularly wide cracks or ones where the two sides are offset out of plane rather than simply separated.
A displaced or rotated brick ledge, or brick courses that are visibly out of level along a wall.
Doors that have progressed from sticking to not latching at all, and door reveals that are out of square — a visible wedge of daylight at the top of a jamb.
Distress concentrated in one area rather than distributed around the house. Uniform minor cracking across a 30-year-old house is age. A cluster of damage at one corner is a localised cause.
Cracked or tented ceramic tile, separation at an interior masonry fireplace, cracks radiating from door and window corners, separated trim joints, cracks in the visible slab edge.
Drainage failures you can see: grade falling toward the foundation, downspouts discharging at the slab, beds that hold water against the house, irrigation heads spraying the veneer.
A large, water-demanding tree close to the slab. This is an established mechanism for localised drying and centre lift, and one of the few causes with a clear, cheap intervention.
What is generally not a foundation finding: hairline shrinkage cracks in a slab edge, minor sheetrock seam cracking, a settled patio joint, or past repairs that appear effective and workmanlike. Concrete shrinks as it cures. Some cracking is the material behaving normally.
Do this before you call anyone
The cheapest useful thing you can do costs nothing and takes twenty minutes.
Photograph every crack and date the photographs. Draw a pencil line at each end of each crack and measure across it. Write down which doors stick and in what month the sticking started. Then recheck after the season turns. A finding that closes up in March was not a structural failure in September.
Then walk the perimeter and look for a gap between the soil and the foundation. Texas A&M AgriLife's guidance treats that gap as the indicator: if there is no gap, soil moisture is adequate; if there is one, the ground around the foundation needs water (AgriLife Extension). The prescription is a soaker hose 8 to 18 inches from the foundation — not against it — run at low pressure for several hours, with a backflow preventer on the faucet, ideally on a timer and a dedicated irrigation zone. Do not water into the crack itself. Consistency is the objective, not saturation.
Fix drainage before you buy piers. Redirecting a downspout and regrading a bed is a few hundred dollars against a repair that runs thousands, and if poor drainage is the driver, piers will not stop it.
Who to call, and in what order
If the indicators are ambiguous, monitor through a wet-dry cycle first.
If they are not ambiguous, call a Texas-licensed professional engineer before you call a repair contractor. Texas does not license foundation repair as a trade — there is no state trade licence for it, and any contractor implying otherwise is misrepresenting the situation. Structural engineers are licensed by the state, they are the only party in this process with a legal obligation that runs to you rather than to a sale, and a contractor's free inspection is a sales visit with a tape measure.
An engineer will also typically call for a plumbing static or hydrostatic test to rule out an under-slab leak first. That matters enormously: a leaking supply or drain line under the slab produces the same symptoms as soil movement and is a completely different repair. Piers installed over an unrepaired leak are money burned.
Ask any engineer's report for two things: an elevation survey with the date, season and recent rainfall context recorded, and an explicit statement of whether the observed condition is progressing. A single undated elevation map is a photograph of a moving object. Two surveys six months apart are evidence. The only absolute way to measure foundation movement is to compare changes between two surveys.
When you do reach the repair stage, ask how the pier spacing in the proposal was derived. The Foundation Performance Association's standard practice sets maximum spacing at 8 feet on centre for one story, 7 for two, 6 for three (FPA-SC-08-1). A bid that spaces piers wider than that, or that cannot tell you why it chose the spacing it did, has not been engineered — it has been priced.